Production of isobutane



Patented May 4, 1943 PRODUCTION OF ISOBUTANE Vladimir N. Ipatiefl' andHerman Pines, Chicago,

Ill., assignors to Universal Oil Products Company, Chicago, 111., acorporation Delaware N'o Drawing. Original application September 30,1936, Serial No. 103,383.

Divided and this appllcation'March 16, 1942, Serial No. 434,904

3 Claims.

This is a division of our co-pending app c tion Serial No. 103,383,filed September 30, 1936.

This invention relates particularly to the treat- ;nentof butane ofnormal or straight-chain strucure.

In a more specific sense, the invention is com cerned with a processwhereby normal butane is converted into isobutane, the process involvingthe use of special catalysts and particular conditions of operationwhich favor the isomerization reactions so that relatively high yieldsof the lso-compound are produced.

Since the invention is concerned principally with the two 4-carbon atomparafiin hydrocarbons and their transformation, one into the other,; thefollowing table is introduced to indicate the structure and theprincipal physical characteristics of these two compounds:

Butanes are produced in considerable quantities in the oil refiningindustry. They occur in gasoline of desirable starting characteristicsaccording to seasonal demands.

The butanes at the present tim bear a further important relationship tooil refining in that their excess production is being utilized as asource of gasoline either by ordinary thermal crackin or by specialcatalytic dehydrogenation processes followed by polymerization in whichcatalysts substantial amounts in natural gases (in which the normalcompound usually predominates), in refinery gases which are evolved fromcrude petroleum storage tanks, and in the primary distillation ofcrudes, and they are also present in considerable percentages in thegases produced incidental to cracking heavy petroleum fractions for theproduction of gasoline. In the case of cracked gas mixtures the relativeproportions of iso and normal butanes va y. but the ratio of the iso tothe normal compound is as a rule considerably higher than in naturalgas.

Butanes may be considered as more or less marginal compounds in respectto their desirability in ordinary gasoline, that is, a certainpercentage of them is essential for sufliclent vapor pressure to insureease in starting, while 'an excess tends to produce vapor lock. Forthese reasons the total percentage of 4-carbon atom hydrocarbons iscommonly adjusted in conjunction with the boiling range and vaporpressure of the other gasoline component to produce a may or may not beused. Investigations have shown that iso-butane is considerably moreamenable to cracking and dehydrogenation, both with and withoutcatalysts, than the normal compound. Considering the correspondingmonoolefins. the normal butenes are considerably more dlflicult topolymerize, either thermally or catalytically, than isO-butene, and itis found also that the octenes representing the dimers of the isobuteneare of higher antiknock value than those from n-butenes which holds alsofor the octanes produced by hydrogenation. It is, therefore, ofconsiderable importance at the present time to convert as much aspossible of, the normal butane production into iso-butane, and hepresent invention is especially concerned with a process foraccomplishing this object.

In one specific embodiment the present invention comprises the treatmentof normal butane for the isomerization thereof into isobutane withcatalysts comprising essentially metallic halides at elevatedtemperatures and superatmospheric pressures.

In a preferred embodiment the catalysts comprise essentially heavy metalchlorides and hydrogen halides.

We have determined that by the use of the class of catalysts mentioned,and particularly by the convenient use" of considerable superatmosphericpressure normal butane may be converted into iso-butane with a. yield ofas high as to Evidently the use of superatmospheric pressures of theorder of 10 to 50 atmospheres at temperatures of C. and higher, besidesdepressing the volatilization of granular catalysts tends also to,depres numerous undesirable side reactions which would result in theformation of. hydrogen and low molecular weight hydrocar- I bons, sothat the reaction proceeds more or less in one direction until anequilibrium is established. 1

There are several alternative catalysts which may be employed inaccomplishing the present isomerization reaction and, while they may beused more or less interchangeably, some are more effective than othersand it is not intended to infer that they are equivalent. Among thecompounds which may be employed may be mentioned aluminum chloride, zincchloride, iron chloride, zirconium chloride, stannic chloride and boronfluoride. Experiments have indicated that best results are obtained whena minor percentage of a hydrogen halide is present in the reactionsalong with these compounds. Some of the compounds may be employed eitherin the dry state or in aqueous solution with suitable modifications ofoperating conditions. In the case of such compounds as aluminumchloride, which readily sublimes, stannic chloride, which boils at 1140., and boron fluoride, which is normally gaseous, these are mostconveniently employed in the anhydrous condition, the hydrogen halides,such as for example hydrogen chloride or bydrofluoric acid, beingseparately introduced in the gaseous state. There will be somevariations in the relative amounts of metal salts and hydrogen halidesused at optimum treating conditions, but the determination of the bestratios is somewhat a matter of experiment.

The process may be operated under batch or continuous conditions.Choosing aluminum chloride and hydrogen chloride as example of jointlyused catalytic materials, batch operations may be conducted byseparately adding aluminum chloride, hydrogen chloride and normal butaneto a closed pressure container, after which the container is agitated orthe contents stirred mechanically while the temperature and pressure areraised by the application of external heat to produce a temperaturecorresponding to maximum production of the iso-compound. This type ofoperation is better adapted to small scale production, and plants ofconsiderable capacity are best operated in a continuous manner. Incontinuous operations the butane may be pumped through a tubular heatingelement at a given temperature and pressure within the approximateranges previously specified and reaction brought about along the line offlow by the separate or joint injection of proportioned amounts of metalsalts and hydrogen halides, the best example of this type or operationbeing the combination of aluminum chloride and hydrogen chloride orboron fluoride and hydrogen fluoride.

In the absence of moisture there will be substantially no corrosion whenusing these substances. After passage through the heating element thereactants may be passed to enlarged insulated chambers for thecompletion of the desired isomerization and the total productssubsequently fractionated to recover catalysts and separate the normaland iso-butanes, after which the normal compound may be recycled forfurther treatment.

Continuous operations may also be conducted by passing normal butanemixed with a hydrogen halide through beds of heated, granular catalyst,which may comprise any of the solid salts mentioned, either alone ormixed with carrying or spacing materials of a relatively inertcharacter. This type of operation is readily utilizable in the case ofsuch compounds as zinc chloride, iron chloride and stannic chloride.Treatment of the products in these cases will involve merely thecondensation of the hydrocarbon products and the recycling of thehydrogen halides for further use.

The following examples are introduced to indicate in a general way thenature of the results obtainable by theme of the process, though theyare not introduced with the intention or correspondingly limiting thescope of the invention.

Example I 100 parts by weight of normal butane, parts by weight ofaluminum chloride and 2 parts by weight of hydrogen chloride wereintroduced under a pressure of about five atmospheres into a pressurevessel, which was then rotated and heated for twelve hour-s at anaverage temperature of 150 C., the maximum pressure developed beingabout 30 atmospheres. After the bomb was cooled the hydrocarbons werereleased and fractionated and it was found. that they consisted of 66.5%of iso-butane and 31.9% of normal butane. This indicates that theequilibrium under these conditions is considerably in favor ofiso-butane.

Example I[ In this operation normal butane was passed through a tubularheating element and then into an enlarged reaction chamber, into whichsublimed aluminum chloride and hydrogen chloride gas were introduced. Apressure of about to atmospheres and a temperature of 160" C. weremaintained on the reaction vessel, after which the reaction productswere separated and it was found that the hydrocarbons consisted of about63% iso-butane and 32% normal butane. This indicates a selectiveconversion of the normal butane into iso-butane under these conditions.

Example 11 I In this case the catalyst employed was a compositeconsisting of about parts by weight of ground pumice and 50 parts byweight of substantially anhydrous zinc chloride. This material wasplaced in a vertical cylindrical reaction chamber which was insulated toconserve heat and the normal butanelwas preheated to a temperature ofapproximately 200 C. and passed downwardly through the contact massunder a pressure of approximately 30 atmospheres. Approximatelyiso-butane and 30% normal butane were found in the reaction products,the remaining 10% comprising lighter fixed gases and other reactionproducts.

Example IV Normal butane was preheated to a temperature of approximatelyC. and passed into an insulated reaction chamber at the same time asboron fluoride and hydrogen fluoride were injected. The reaction chamberwas nickel-lined, as this was found to further accelerate theisomerization reactions. An analysis of the hydrocarbon products showedthat they consisted of approximately 62% by weight of iso-butane and 32%by weight of normal butane, the remaining products being lighter gasesand some heavier polymerized products.

The character of the present invention and its value commercially havebeen shown respectively by the foregoing specification and examplesintroduced although the proper scope of the invention is not limited inexact correspondence with the descriptive o r numerical sections.

We claim as our invention:

l. A process for producing iso-butane which comprises subjecting normalbutane to the action of boron fluoride in the presence of metallicnickel under conditions and in the presence of an amount of hydrogenhalide such that isomeriza- 7 2,318,226 tion of normal butaneconstitutes the principal reaction of the process.

2. A process for producing iso-butane which comprises passing normalbutane, hydrogen fluoride, and boron fluoride through a reaction zonecontaining metallic nickel therein maintained under isomerizingconditions. said conditions and the amount of hydrogen fluoride beingsuch that

